Generally, an ultraviolet light-emitting diode (UV LED) has a multi-layer structure made of different materials. The selection of materials and thicknesses affects the LED light-emitting wavelength. To improve extraction efficiency, the multi-layer structure comprises different chemical components to facilitate independent entry of photocurrent carrier into the recombination region (in general, the quantum well). The quantum well side is added with donor atoms to increase the electron concentration (the N-type layer) and the other side is added with acceptor atoms to increase the hole concentration (the P-type layer).
The UV LED also comprises an electronic contact structure. Different electrode structures are selected for power connection based on properties of different devices. The power can provide current for devices through the contact structure. The contact structure injects the current into the light-emitting layer along the device surface and transfers current to light. The contact structure on the UV LED surface can be made of conducting material. Good ohmic contact can reduce contact resistance. However, those structures may prevent the light from emitting, thereby reducing the luminous flux. As shown in FIG. 1, a UV LED structure. The p-GaN layer of the epitaxial covering layer over the surface has a band gap of 3.4 eV (364 nm) and absorbs the UV less than 364 nm from the light-emitting region.
As shown in FIG. 2, a flip-chip light-emitting structure that can solve light absorption problem of the p-GaN layer. In the flip-chip structure, the reflection efficiency of the reflecting layer is of great importance to the light-emitting efficiency. The work function of the metal reflecting layer and the Schottky barrier height difference of the light-emitting epitaxial layer determine the ohmic contact performance between the reflecting layer and the conductive interface. To form a low-resistance ohmic contact, the ohmic contact layer on the P-type semiconductor adopts metal of high work function and high UV reflectivity. Metal of good reflectivity in the UV region, generally, belongs to low work function metal (for example, Al has good reflectivity in the UV region and the work function is 4.28 eV. It belongs to low work function metal). For existing P-type ohmic contact metal, it is necessary to adopt metal of high work function (e.g., Cr, Ni or Ti) as the medium layer to improve the ohmic contact of the p-type layer. However, the Cr, Ti and Ni have extremely poor reflectivity for UV with wavelength less than 380 nm.